Fin structure formation

ABSTRACT

A method for forming fin structures is provided. Sacrificial structures are provided on a substrate. Fin structures are formed on the sides of the sacrificial structures. The forming of the fin structures comprises a plurality of cycles, wherein each cycle comprises a fin deposition phase and a fin profile shaping phase. The sacrificial structure is removed.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.More particularly, the invention relates to the formation ofsemiconductor devices with fin structures.

In a semiconductor-based device (e.g., integrated circuits or flat paneldisplays), fin structures may be used in various devices. For example, afinFET is a MOSFET built on a SOI substrate on which silicon is etchedinto a fin shaped body of the transistor. A gate is wrapped around andover the fin structure.

Spacer lithography may be one way of creating fins. In one way of doingthis, a sacrificial layer is provided and then etched to formsacrificial structures. A conformal CVD is then used to form a conformallayer over and around the sacrificial structures. An etch back is usedto etch the horizontal layers of the conformal layer. The sacrificialstructure is then removed to form fin structures. The thickness of thefins may be 10 nm or less. To provide a desired conformal layer, theconventional CVD deposition may require a high temperature CVD. Suchhigh temperatures may be detrimental to the semiconductor device. Thehigh temperature may cause a process to go beyond a device thermalbudget. In addition, if doping has previously been done, the hightemperature may be detrimental to the doped areas.

In addition, such CVD fin processes are limited with regards to thesacrificial layer and fin. Generally, a sacrificial layer of siliconoxide would provide a fin of silicon nitride. A sacrificial layer ofsilicon nitride would provide a sacrificial layer of silicon oxide.

Furthermore, forming fin structures with conformal CVD processes placesvery stringent requirements on the profile of the sacrificialstructures. The profile angle would need to be very close to vertical. Aslight deviation from vertical profile would cause the fin structure totilt, causing potential defect problems and CD variations.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for forming fin structures is provided.Sacrificial structures are provided on a substrate. Fin structures areformed on the sides of the sacrificial structures. The forming of thefin structures comprises a plurality of cycles, wherein each cyclecomprises a fin deposition phase and a fin profile shaping phase. Thesacrificial structure is removed.

In another manifestation of the invention, a method for forming aplurality of vertical fins on a substrate is provided. Sacrificialstructures are provided on the substrate. Fin structures are formed onthe sides of the sacrificial structures, comprising a plurality ofcycles. Each cycle comprises a fin deposition phase, which deposits afin material, and a fin profile shaping phase, which shapes the profileof the deposited fin material. The fin deposition phase comprisesproviding a deposition gas, forming a plasma from the deposition gas,depositing deposition material to form fins, and stopping the flow ofthe deposition gas. The fin profile shaping phase comprises providing aprofile shaping gas different than the deposition gas, forming a plasmafrom the profile shaping gas, shaping the profile of the depositeddeposition material, and stopping the flow of the profile shaping gas.The sacrificial structure is removed.

In another manifestation of the invention, an apparatus for forming finstructures is provided. A plasma processing chamber comprising a chamberwall forming a plasma processing chamber enclosure, a substrate supportfor supporting a substrate within the plasma processing chamberenclosure, a pressure regulator for regulating the pressure in theplasma processing chamber enclosure, at least one electrode forproviding power to the plasma processing chamber enclosure forsustaining a plasma, a gas inlet for providing gas into the plasmaprocessing chamber enclosure, and a gas outlet for exhausting gas fromthe plasma processing chamber enclosure is provided. A gas source is influid connection with the gas inlet. The gas source comprises asacrificial layer etchant source, a fin deposition gas source, and a finprofile shaping gas source. A controller is controllably connected tothe gas source and the at least one electrode. The controller comprisesat least one processor and computer readable media. The computerreadable media comprises computer readable code for providingsacrificial structures on the substrate, computer readable code forforming fin structures on the sides of the sacrificial structures,comprising a plurality of cycles, and computer readable code forremoving the sacrificial structure. The computer readable code forforming fin structures comprises computer readable code for providing aplurality of cycles, wherein each cycle comprises a fin deposition phasewhich deposits a fin material, comprising computer readable code forproviding a deposition gas, computer readable code for forming a plasmafrom the deposition gas, computer readable code for depositingdeposition material to form fins, and computer readable code forstopping the flow of the deposition gas, and a fin profile shaping phasewhich shapes the profile of the deposited fin material, comprisingcomputer readable code for providing a profile shaping gas differentthan the deposition gas, computer readable code for forming a plasmafrom the profile shaping gas, computer readable code for shaping theprofile of the deposited deposition material, and computer readable codefor stopping the flow of the profile shaping gas.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIG. 2 is a more detailed flow chart of the forming sacrificialstructures.

FIGS. 3A-F are schematic cross-sectional and top views of a stackprocessed according to an embodiment of the invention.

FIG. 4 is a schematic view of a plasma processing chamber that may beused in practicing the invention.

FIGS. 5A-B illustrate a computer system, which is suitable forimplementing a controller used in embodiments of the present invention.

FIG. 6 is a more detailed flow of a step of fin formation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess that may be used in an embodiment of the invention. Sacrificialstructures are formed (step 104). Fins are formed on the side of thesacrificial structures (step 108). FIG. 6 is a more detailed flow chartof the forming fins on the side of the sacrificial structures, whichcomprises a plurality of cycles, wherein each cycle comprises a findeposition phase (step 604) and a fin profile shaping phase (step 608).The sacrificial structures are removed (step 112).

EXAMPLE 1

In an example of an embodiment of the invention, the sacrificialstructures are formed (step 104). FIG. 2 is a more detailed flow chartof the formation of the sacrificial structures. A sacrificial layer isformed (step 204). FIG. 3A is a cross-sectional view of a stack 300 witha sacrificial layer 312 formed over a substrate 304. One or more layerssuch as an intermediate layer 308 may be between the sacrificial layer312 and the substrate 304. In this example, the substrate 304 is asilicon wafer. The sacrificial layer may be of a wide assortment ofmaterials such as silicon nitride (SiN), photoresist, silicon oxide(SiO₂), amorphous carbon, silicon, or organic material. The sacrificiallayer is silicon carbide. In other embodiments, the sacrificial layer isat least one of SiC, SiN, SiOC, H doped SiOC, TiN, TaN, Ti, Ta, Si, andSiO2. More generally, the sacrificial layer is of any material, whichmay be selectively etched with respect to a fin material and anyunderlying layer.

A mask 314 is formed over the sacrificial layer 312 (step 208), as shownin FIG. 3B. Features 316 are etched into the sacrificial layer 312 (step212), as shown in FIG. 3C. After etching features in the sacrificiallayer, the mask 314 is removed (step 216), as shown in FIG. 3D. It ispreferred that the feature sides have a slightly re-entrant profile sothat the etched features are wider at the bottom than at the top to givethe resulting fin structure a slightly tapered profile. Preferably, theetched features 316 have sides with a profile angle that is 89 to 95degrees. Most preferably, the profile angle of the sides of the etchedfeatures ranges from 90 to 93 degrees.

Fins 324 are formed on the sides of the sacrificial structures formed bythe remaining sacrificial layer 312 (step 108), as shown in FIG. 3E.

FIG. 4 is a schematic view of a processing chamber 400 that may be usedto form the fins. The plasma processing chamber 400 comprisesconfinement rings 402, an upper electrode 404, a lower electrode 408, agas source 410, and an exhaust pump 420. The gas source 410 comprises afin deposition gas source 412 and a fin profile shaping gas source 416.The gas source may comprise additional gas sources such as an etch gassource 418 to allow etching of the sacrificial layer to be done in situin the same chamber. Within plasma processing chamber 400, the substrate304 is positioned upon the lower electrode 408. The lower electrode 408incorporates a suitable substrate chucking mechanism (e.g.,electrostatic, mechanical clamping, or the like) for holding thesubstrate 304. The reactor top 428 incorporates the upper electrode 404disposed immediately opposite the lower electrode 408. The upperelectrode 404, lower electrode 408, and confinement rings 402 define theconfined plasma volume 440. Gas is supplied to the confined plasmavolume by the gas source 410 and is exhausted from the confined plasmavolume through the confinement rings 402 and an exhaust port by theexhaust pump 420. A first RF source 444 is electrically connected to theupper electrode 404. A second RF source 448 is electrically connected tothe lower electrode 408. Chamber walls 452 surround the confinementrings 402, the upper electrode 404, and the lower electrode 408. Boththe first RF source 444 and the second RF source 448 may comprise a 27MHz power source and a 2 MHz power source. Different combinations ofconnecting RF power to the electrode are possible. In the case of LamResearch Corporation's Dual Frequency Capacitive (DFC) System, made byLAM Research Corporation™ of Fremont, Calif., which may be used in apreferred embodiment of the invention, both the 27 MHz and 2 MHz powersources make up the second RF power source 448 connected to the lowerelectrode, and the upper electrode is grounded. In other embodiments,the RF power source may have a frequency up to 300 MHz. A controller 435is controllably connected to the RF sources 444, 448, exhaust pump 420,and the gas source 410.

FIGS. 5A and 5B illustrate a computer system 1300, which is suitable forimplementing a controller 435 used in embodiments of the presentinvention. FIG. 5A shows one possible physical form of the computersystem. Of course, the computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. Computer system 1300includes a monitor 1302, a display 1304, a housing 1306, a disk drive1308, a keyboard 1310, and a mouse 1312. Disk 1314 is acomputer-readable medium used to transfer data to and from computersystem 1300.

FIG. 5B is an example of a block diagram for computer system 1300.Attached to system bus 1320 is a wide variety of subsystems.Processor(s) 1322 (also referred to as central processing units, orCPUs) are coupled to storage devices, including memory 1324. Memory 1324includes random access memory (RAM) and read-only memory (ROM). As iswell known in the art, ROM acts to transfer data and instructionsuni-directionally to the CPU and RAM is used typically to transfer dataand instructions in a bi-directional manner. Both of these types ofmemories may include any suitable of the computer-readable mediadescribed below. A fixed disk 1326 is also coupled bi-directionally toCPU 1322; it provides additional data storage capacity and may alsoinclude any of the computer-readable media described below. Fixed disk1326 may be used to store programs, data, and the like and is typicallya secondary storage medium (such as a hard disk) that is slower thanprimary storage. It will be appreciated that the information retainedwithin fixed disk 1326 may, in appropriate cases, be incorporated instandard fashion as virtual memory in memory 1324. Removable disk 1314may take the form of any of the computer-readable media described below.

CPU 1322 is also coupled to a variety of input/output devices, such asdisplay 1304, keyboard 1310, mouse 1312, and speakers 1330. In general,an input/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU1322 optionally may be coupled to another computer or telecommunicationsnetwork using network interface 1340. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 1322 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

FIG. 6 is a more detailed flow chart of the forming fins on the side ofthe sacrificial structures, which comprises a plurality of cycles,wherein each cycle comprises a fin deposition phase (step 604) and a finprofile shaping phase (step 608).

Preferably, the fin deposition phase (step 604) uses a deposition gascomprising at least one of a combination of CF₄ and H₂ or a combinationof CH₃F and N₂ or C_(x)F_(y) or C_(x)H_(y)F_(z) or C_(x)H_(y) with anoxidizing or reducing additive such as hydrogen, nitrogen, or oxygen,and carrier gases such as He, Ar, Ne, Kr, Xe etc. More generally, thedeposition gas comprises at least one of hydrocarbon, fluorocarbon, andhydrofluorocarbon, silane or any Si-containing gases. More preferably,the deposition gas further comprises a carrier gas, such as argon orxenon. More preferably, the deposition gas further comprises at leastone of an oxidizing additive and a reducing additive, such as O₂, H₂, orNH₃.

An example of a fin deposition phase (step 604) provides a flow of 150sccm CH₃F, 75 sccm N₂, and 100 sccm Ar. The pressure is set to 80 mTorr.The substrate is maintained at a temperature of 20° C. The second RFsource 448 provides 400 Watts at a frequency of 27 MHz and 0 Watts afrequency of 2 MHz. During the deposition phase the deposition gas isprovided, the deposition gas is transformed into a plasma, and then thedeposition gas is stopped.

Preferably, the fin profile shaping stage uses a profile shaping gascomprising at least one of C_(x)F_(y) and NF₃ and C_(x)H_(y) andC_(x)H_(y)F_(z). More preferably, the profile shaping gas furthercomprises a carrier gas, such as argon or xenon. More preferably, theprofile shaping gas further comprises at least one of an oxidizingadditive and a reducing additive, such as O₂, H₂, or NH₃. As a result,the profile shaping gas is different than the deposition gas.

An example of the fin profile shaping phase (step 608) provides ahalogen (i.e. fluorine, bromine, chlorine) containing hydrocarbon gas,such as 100 sccm CF₄. In this example, CF₄ is the only gas providedduring the profile shaping. A pressure of 20 mTorr is provided to thechamber. The second RF source 448 provides 600 Watts at a frequency of27 MHz and 0 Watts a frequency of 2 MHz. During the profile shapingphase the profile shaping gas is provided, the profile shaping gas istransformed into a plasma, and then the profile shaping gas is stopped.

Preferably, the process is performed for between 2 to 20 cycles. Morepreferably, the process is performed between 3 to 10 cycles. Thecombination of deposition and profile shaping over a plurality of cyclesallows for the formation of vertical sidewalls for the fins. Preferably,the vertical sidewalls are sidewalls that from bottom to top make anangle between 87° to 93° with the bottom of the fins. When combined witha slightly re-entrant profile on the sacrificial structures, asymmetrically slightly tapered fin structure is formed.

The cyclical cycle may have additional deposition and/or shaping phasesor may have other additional phases for the formation of the fins.

The sacrificial structures are then removed (step 112), leaving theremaining fins 324 as shown in FIG. 3F.

EXAMPLE 2

In another example, the formation of a sacrificial structures 104, aphotoresist mask itself may be used as a sacrificial structure, so thatan additional sacrificial layer is not used.

In both examples, additional conventional processing steps are providedto form finFETs out of the fins.

The inventive process provides fins of various materials such asamorphous carbon, amorphous silicon, silicon oxide, and silicon nitride.

While this invention has been described in terms of several preferredembodiments, there are alterations, modifications, permutations, andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, modifications, permutations, andvarious substitute equivalents as fall within the true spirit and scopeof the present invention.

1. A method, comprising: providing sacrificial structures on asubstrate; forming fin structures on sides of the sacrificialstructures, comprising a plurality of cycles, wherein each cyclecomprises: a fin deposition phase; and a fin profile shaping phase; andremoving the sacrificial structure.
 2. The method, as recited in claim1, wherein the fin deposition phase comprises: providing a depositiongas; forming a plasma from the deposition gas; depositing a depositionmaterial from the plasma to form fins; and stopping the flow of thedeposition gas.
 3. The method, as recited in claim 2, wherein the finprofile shaping phase comprises: providing a profile shaping gasdifferent than the deposition gas; forming a plasma from the profileshaping gas; shaping profiles of the deposited deposition material; andstopping the flow of the profile shaping gas.
 4. The method, as recitedin claim 3, wherein the deposition gas comprises at least one of ahydrocarbon, fluorocarbon, hydrofluorocarbon, silane, and aSi-containing gases and the profile shaping gas comprises at least oneof C_(x)F_(y), NF₃, C_(x)H_(y) and C_(x)H_(y)F_(z).
 5. The method, asrecited in claim 4, wherein the fin structures have vertical sidewalls.6. The method, as recited in claim 5, wherein the providing sacrificialstructures comprises forming a photoresist mask over the substrate,wherein the photoresist mask forms the sacrificial structures.
 7. Themethod, as recited in claim 5, wherein the providing sacrificialstructures comprises: forming a sacrificial layer over the substrate,forming a mask over the substrate; etching features into the sacrificiallayer through the mask; and removing the mask.
 8. The method, as recitedin claim 7, wherein the mask is a photoresist mask.
 9. The method, asrecited in claim 1, wherein the fin structures have vertical sidewalls.10. The method, as recited in claim 1, wherein the providing sacrificialstructures comprises forming a photoresist mask over the substrate,wherein the photoresist mask forms the sacrificial structures.
 11. Themethod, as recited in claim 1, wherein the providing sacrificialstructures comprises: forming a sacrificial layer over the substrate,forming a mask over the substrate; etching features into the sacrificiallayer through the mask; and removing the mask.
 12. The method, asrecited in claim 11, wherein the mask is a photoresist mask.
 13. Adevice formed by the method of claim
 1. 14. A method for forming aplurality of vertical fins on a substrate, comprising: providingsacrificial structures on the substrate; forming fin structures on sidesof the sacrificial structures, comprising a plurality of cycles, whereineach cycle comprises: a fin deposition phase which deposits a finmaterial, comprising: providing a deposition gas; forming a plasma fromthe deposition gas; depositing deposition material to form fins; andstopping the flow of the deposition gas; and a fin profile shaping phasewhich shapes the profile of the deposited fin material, comprising:providing a profile shaping gas different than the deposition gas;forming a plasma from the profile shaping gas; shaping the profile ofthe deposited deposition material; and stopping the flow of the profileshaping gas; and removing the sacrificial structure.
 15. The method, asrecited in claim 14, wherein the deposition gas comprises at least oneof a hydrocarbon, fluorocarbon, hydrofluorocarbon, silane, and aSi-containing gases and the profile shaping gas comprises at least oneof C_(x)F_(y), NF₃, C_(x)H_(y) and C_(x)H_(y)F_(z).
 16. The method, asrecited in claim 14, wherein the fin structures have vertical sidewalls.17. The method, as recited in claim 14, wherein the providingsacrificial structures comprises forming a photoresist mask over thesubstrate, wherein the photoresist mask forms the sacrificialstructures.
 18. The method, as recited in claim 14, wherein theproviding sacrificial structures comprises: forming a sacrificial layerover the substrate, forming a mask over the substrate; etching featuresinto the sacrificial layer through the mask; and removing the mask. 19.The method, as recited in claim 18, wherein the mask is a photoresistmask.